Hello all,
I am an infrequent poster, and once in a while do some reading here.
I have a sea kayaking background, do also K1 masters races and want to start surf skiing. My two daughters (10 and 12) both race (M)K1s, and have a longing for waves and open water as well. So I would like to have a sirfski for the girls, but for paddlers between 35 and 45 kg not a lot is available. So I am working on a design for them, and want to use this to test an experimental building method I want to try. (strip playing with vertical strips in foam, and covering inside and outside with glass / carbon using resin infusion, but that is another story.)

I am working on two design ideas. One with the width carried more along the length of the boat, the other with the widest point behind the cockpit. Both are very similar regarding estimated speed (KAPER algorithm) and stability. Both are shown in the attached images.
The bows still will change, as Kayak Foundry has limited accuracy in the generation of steep bows without concavities. Moving the design to Rhino will take care of that. I also attach a preliminary Rhino image of an earlier design, this shows the change in bow form a bit.

Design goals were:
Sufficient stability (for K1 trained kids)
low wetted surface area
Paddler weight 35 to 45 kg
Limited length (to keep wetted area low)
High prismatic coefficient (to reduce wave making resistance at higher speeds
The trade off between the designs is having a slightly wider catch (about 1 to 2 cm), versus a relatively wide and flat stern. I am worried about the behaviour of that wide flat stern in quartering waves.

Some images:
Wider in the stern:

More even width distribution

Example rendering in Rhino (still a lot of work to do here, I am learning Rhino)

Things I still am doubting about are rocker and width distribution. Any other advice is welcome of course.

Another doubt of mine is if it isn't a better idea to start with a ski for myself. I will spend quite some time on a completed ski (estimated ~ 160 hrs) and I am not sure how much the kids will use it. I really want to own a ski myself, but the EPIC and Thinks are getting priced out of my league, with only the Stellars somewhat affordable. I will be able to build a complete carbon ski for about 1600 euros, that is about half of what a commercial ski costs. And I will learn a lot in the process.